2.1. The Complement System
The complement system is a group of proteins that constitutes about 10 percent of the globulins in the normal serum of humans (Hood, L. E., et al., 1984, Immunology, 2d Ed., The Benjamin/Cummings Publishing Co., Menlo Park, Calif., p. 339). Complement (C) plays an important role in the mediation of immune and allergic reactions (Rapp, H. J. and Borsos, T, 1970, Molecular Basis of Complement Action, Appleton-Century-Crofts (Meredith), New York). The activation of complement components leads to the generation of a group of factors, including chemotactic peptides that mediate the inflammation associated with complement-dependent diseases. The sequential activation of the complement cascade may occur via the classical pathway involving antigen-antibody complexes, or by an alternative pathway which involves the recognition of certain cell wall polysaccharides. The activities mediated by activated complement proteins include lysis of target cells, chemotaxis, opsonization, stimulation of vascular and other smooth muscle cells, and functional aberrations such as degranulation of mast cells, increased permeability of small blood vessels, directed migration of leukocytes, and activation of B lymphocytes and macrophages (Eisen, H. N., 1974, Immunology, Harper & Row Publishers, Inc. Hagerstown, Md., p. 512).
During proteolytic cascade steps, biologically active peptide fragments, the anaphylatoxins C3a, C4a, and C5a (See WHO Scientific Group, 1977, WHO Tech. Rep. Ser. 606:5 and references cited therein), are released from the third (C3), fourth (C4), and fifth (C5) native complement components (Hugli, T. E., 1981, CRC Crit. Rev. Immunol. 1:321; Bult, H. and Herman, A. G., 1983, Agents Actions 13:405).